HOUSTON - NASA has pushed back the
planned launch of the final flight to overhaul the Hubble Space Telescope by up
to five weeks due to external fuel tank delays, mission managers said Thursday.

Space shuttle program manager John
Shannon said that the additional time required to include post-Columbia safety
improvements in two shuttle fuel tanks supporting the Hubble
servicing mission have delayed the spaceflight to no earlier than late
September. A seven-astronaut crew was slated to launch toward Hubble aboard
NASA?s shuttle Atlantis on Aug. 28.

?We really cannot make that date
with the external tank processing,? Shannon told reporters in a briefing here
at NASA?s Johnson Space Center. ?I really think it?s a small price to pay, to
tell you the truth, four to five weeks for all the improvements that we?re
getting on this tank.?

Atlantis? next fuel tank, and a
second reserved for a rescue shuttle, are NASA?s first built from scratch that
include modifications to limit the loss of foam insulation that could damage an
orbiter during liftoff. Foam debris gouged a hole in the shuttle Columbia?s
left wing during its 2003 launch that led to the loss of the orbiter and its
seven-astronaut crew as they reentered the Earth?s atmosphere.

Since then, NASA has modified
existing shuttle fuel tanks and required in-space inspections of orbiter heat
shields to ensure they are in good health.

The agency required two of the new
external tanks for the Hubble
servicing flight because Atlantis astronauts will be unable to take refuge
aboard the International Space Station (ISS) if their spacecraft suffers severe
damage since the two destinations are in different orbits. Instead, a second
shuttle - Endeavour - will be prepared to serve as a rescue ship.

The Hubble mission?s delay also
means NASA will have to push back a subsequent flight to haul new equipment to
the International Space Station (ISS) and likely fly only five of the six
shuttle flights originally slated for 2008, Shannon said. The ripple effect is
not expected to impact NASA?s plans to complete space station construction and
retire the shuttle fleet by 2010, he added.

While shuttle officials prepare for
Discovery?s launch, NASA station managers and their Russian counterparts have
canceled a short Soyuz flight outside the ISS as investigators hunt for the
source of a malfunction that sent anearlier
spacecraft off-course during its April landing.

The Russian-built Soyuz TMA-11
spacecraft landed on the central Asian steppes of Kazakhstan on April 19, but
reentered the Earth?s atmosphere at a steeper angle than normal and subjected
its crew to higher gravitational loads. The Soyuz returned NASA astronaut Peggy
Whitson, Russian cosmonaut Yuri Malenchenko and South Korean spaceflyer So-yeon
Yi - who
has since been hospitalized due to back and neck pain - to Earth after
their station flights.

The spacecraft appears to have
suffered a glitch during the separation of its crew capsule and propulsion
module. A similar reentry malfunction afflicted a returning Soyuz spacecraft
last October, prompting Russian engineers to take a new look at both
malfunctions.

?We really need to let this
commission finish their work to decide what the cause of the anomaly was before
we understand whether the crew was subjected to any additional risk,? said Mike
Suffredini, NASA?s space station program manager.

Space station commander Sergei
Volkov and two crewmates were slated to move their own Soyuz TMA-12 spacecraft
two a new docking port next week. But NASA and Russian mission managers opted
to cancel the orbital trip on the off-chance that Volkov and his crew were
unable to redock with the station, and forced to return to Earth while the
investigation was still under way.

?We just wanted to not expose
ourselves to that small risk,? said Suffredini, adding that the Soyuz is still
clear to return Volkov and his crew to Earth in the event of a major emergency.

Russian engineers expect to complete
their investigation by the end of the month.

?We?re going to have to give them
some time to work through the data,? Suffredini said.